Silicene finally comes unstuck

For some time, researchers have been stuck on silicene — literally. Silicene, the thinnest possible form of silicon, comprises a two-dimensional layer of silicon crystals and is heralded as the key to even smaller, more flexible, transparent and low-energy-cost electronics.

But the problem with silicene is that, until now, it has been ‘grown’ on a metal surface — and researchers had no way of freeing it from the substrate to create a freestanding material that could then be incorporated into electronic devices and components.

Dr Yi Du and his team at the University of Wollongong’s Institute for Superconducting and Electronic Materials (ISEM) have used oxygen to separate a single-atom-thick layer of silicon from its surface, overcoming the key hurdle preventing the production of a material with potential to supercharge electronics.

“We know silicene crystals prefer to firmly attach on the metallic substrate and because they are too thin to be peeled off by any mechanical tools, it’s impossible to remove them from the substrate,” Dr Du said.

Researchers have experimented with the idea of using ‘chemical scissors’ to break the bond between silicene and the substrate and the breakthrough for Dr Du and his team came through using oxygen molecules as chemical scissors to cut the silicene from its substrate.

The work involves several special techniques that can be done only at ISEM with the help of its powerful tools, including a scanning tunnelling microscope, which creates an ultrahigh vacuum environment about a hundred times higher than the vacuum level experienced in orbit at the International Space Station.

“Because the vacuum levels are so high, we can inject the oxygen molecules into the chamber and they become a ‘molecular flux’ that follows a straight pathway,” Dr Du said.

“This allows us to direct these molecules precisely into the silicene layers, acting like scissors to separate the silicene.”

The result is a layer of freestanding silicene — with an appearance much like a honeycomb lattice — that could be transferred to an insulating substrate to make advanced transistors.

“This work solves the long-lasting problem of isolating this super material for further device development. It challenges the entire scientific literature on silicene since its discovery,” Dr Du said. “These findings are relevant for the future design and application of silicene-based nanoelectronic and spintronic devices.”

The research was published in the journals Science Advances and ACS Central Science.